Metal rolling, such as high-speed rolling, is a metalworking process used for producing metal strip. Resulting metal strip can be coiled, cut, machined, pressed, or otherwise formed into further products, such as beverage cans, automotive parts, or many other metal products. Metal rolling involves passing metal (e.g., a metal strip) through one or more mill stands, each having one or more work rolls that compress the metal strip to reduce the thickness of the metal strip. Each work roll can be supported by a backup roll.
During metal rolling, such as high-speed metal rolling, self-excited vibrations can occur on resonant frequencies of the mill. Specifically, each mill stand can vibrate in its own self-excited vibration. Self-excited vibration can be very prevalent in or around the range of approximately 100 Hz to approximately 300 Hz. This type of self-excited vibration can be known as “Third Octave” vibration because the frequency band of the mill's vibration coincides with the third musical octave (128 Hz to 256 Hz). This self-excited third octave vibration is self-sustaining vibration produced by the interaction between the rolls' spreading forces and the entry strip tension (e.g., tension of the strip in the direction of rolling as the strip enters the mill stand). Self-excited third octave vibration does not require energy to be delivered at the resonant frequency in order to excite the mill stand's natural resonance.
Self-excited third octave vibration can cause various problems in a mill. If left unchecked, self-excited third octave vibration can damage the mill stand itself, including the rolls, as well as damage any metal being rolled, rendering the metal unusable, and therefore scrap. Attempts have been made to counter self-excited third octave vibration by slowing the rolling speed the moment self-excited third octave vibration is detected. Such approaches can still cause wear to the mill stand and damage to the metal strip being rolled in small amounts, and can significantly slow the process of rolling the metal strip, reducing possible output of the mill.